A comparison between baseballs used in MLB and NPB


Many pixels have been spilled about the adjustments Japanese pitchers must make in the transition to American baseball. Most of the attention is focused on the differences in the official baseballs used in the major Japanese (NPB) and American (MLB) professional leagues. The differences in physical dimensions between those baseballs have been of particular interest. This has become a focal point locally after the Cubs signed Shōta Imanaga, an elite mound coming off eight seasons of very good pitching in the NPB.

What we are attempting here is to examine the differences in dimensions using samples readily available for purchase and inspection. We will not attempt to compare manufacturing methods, internal composition or relative pre-play treatments of leather surfaces. That is a very different topic.

An overview of MLB baseball is in order. The physical dimensions of the ball have been one of the immutable aspects of the American game. They are covered in Rule 3.01: “Shall weigh not less than 5 nor more than 5¼ ounces and measure not less than 9 nor more than 9¼ inches in circumference.” These were established by the National Association (1871-75) in 1872 and have since been adopted by all their professional successors. In its initial season, the Association had no standards and decreed that the home team supply the game balls for all competitions. When the inevitable abuses arose, the rules we now know were established.

All baseballs illustrated for this article are from the author’s personal collection.

FIGURE 1: An official MLB ball, game used at Wrigley Field in 2022. Circumference 9¼ inches. This is the maximum limit according to MLB rules.

FIGURE 2: An official MLB ball, also used at Wrigley in 2022. Circumference 9.00 inches, the minimum limit under the rules.

FIGURE 3: The two baseballs side by side, with guides for comparison. This is the tolerance difference allowed under MLB rules. I have no doubt that a professional player can tell the difference, and how often do you see a pitcher ask an umpire for a different baseball, after being handed a new one?

Unlike MLB, which has had a designated supplier of official balls since the beginning (the current supplier, Rawlings, has held the MLB contract since 1977), the NPB did not use an official supplier until 2009. Before that, each The team used baseballs manufactured by multiple manufacturers, approved after inspection by the NPB office. These baseballs bore no fingerprints except the NPB seal of approval; the providers were essentially anonymous. As in the United States more than a century earlier, questionable aspects of this practice forced NPB to adopt a more formal supply chain. Mizuno has made official NPB baseballs since 2009.

FIGURE 4a/b: A pre-Mizuno approved NPB baseball, purchased in 1995 at the Yakult Swallows team store. Circumference 9⅛ inches.

FIGURE 5a/b: Current official Mizuno NPB baseball, purchased from Mizuno in 2024. Circumference 9⅛ inches.

FIGURE 6: Official MLB and NPB baseballs in a row, with guides to compare. (Larger version of the image here)

NPB specimens, although manufactured by different suppliers nearly three decades apart, have remained remarkably similar. Some recent articles have indicated circumferences for NPB baseballs as small as 8⅞ inches. If the NPB balls illustrated here can be considered to represent the upper limits within their rules, they are within MLB tolerances. Even the NPB’s minimum standards would differ very little from those of the MLB. It should be noted that all baseballs used in the World Baseball Classic tournaments have been manufactured by Rawlings and have used MLB standards for size and weight. Therefore, Japanese players were certainly familiar with the use of MLB baseball in elite competitions.

One easily visible difference is in the seams; I would dare say that the difference is more significant than the difference in size. The NPB seams are noticeably smaller and therefore form a greater distance at the points where they are closest together (the so-called “sweet spots”). Both baseballs use 108 pairs of dots. 108 pairs have been the standard in the MLB since 1919, previously the number was 116 and the first baseballs even more so.

It is widely believed that smaller seams provide better grip overall. Personal touch inspection also confirms that the surface of NPB baseballs is “stickier” than that of MLB, whose factory-fresh product has always been noted for its slipperiness. Both leagues use pre-game treatments aimed at increasing finger grip.

This ends the NPB/MLB visual comparisons. They have in it.

And now something (more or less) completely different. As regular readers know, Al LOVES research. So here’s a detective using some older spheres.

1930 was a historic offensive year in the MLB. The entire National League hit .303, Bill Terry became the last National League hitter to hit .400, Hack Wilson set a National League home run record that stood until steroids, as well as a record for runs batted in. for the MLB that may never be broken and only the Washington Senators posted a team ERA below 4.00. The Philadelphia Phillies posted a .315 batting average and a 6.71 ERA. So what happened? As has been happening since time immemorial, baseballs did it, or so they say.

Conspiracy theorists (i.e., pitchers in 1930) maintained that it was not that the baseball was squeezed, but rather that the seams were sagging, making it nearly impossible to effectively throw the (relatively few) breaking pitches of baseball. The time. Let’s take a look.

To do this, we must reliably date the game balls to a specific year. Since footprints often do not vary over long periods of time, how can this be done? Leaving with official balls signed by the team. A baseball signed by an entire team, or close to it, can be dated to a specific year through chart comparisons.

The baseballs used in this illustration are team-signed baseballs dating from the years in question. They are photographed to show the official prints, the signatures, for the most part, are not visible. It should be noted that American League and National League baseballs were manufactured by the same company (Spalding), although the Reach brand was used for American League baseballs. Spalding had acquired Reach in 1889, but continued to use the Reach brand for several decades.

FIGURE 7: LR, 1929 AL, 1930 AL, 1931 NL. What is immediately obvious is that there was a reaction in 1931. The threads in the seams are heavier, the seams themselves are larger. In fact, the size of the seams and the thickness of the thread is the same as today’s baseballs. Beginning in 1931, MLB baseballs have a modern appearance, except for the color of the threads.

It all comes down to the difference between 1929 and 1930. The overall size of the stitching and threading is the same, the difference, and it may be hard to see in the photos, is that the slots cut into the leather for threading are deeper. at the 1930 ball. The threads themselves do not rise above the surface of the leather. If there is a discernible difference, it is this.

Of course, one would prefer many more specimens to provide a more representative sample, but this will simply have to suffice.

One more.

FIGURE 8: LR, 1932 NL, 1933 NL, 1934 NL, all balls signed by the Cubs team. This represents the transition to the modern look. Until 1934, the thread was blue and red for American League baseballs, and black and red for National League baseballs. In 1934, both leagues turned red. Surviving correspondence between MLB and Spalding suggests this was an economic measure. Nothing is new under the sun.

It could have been profitable, but something was lost in translation. Thank you very much for all the attention.


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